Cellular therapy is becoming an interesting addition for medical therapies for repairing, restoring or ameliorating function of tissues and particularly combining with traditional surgical techniques. Some cell choices are more adaptable to cellular therapy in patients. Tissue choices from animal and human at all ages of development can be evaluated with advantages and disadvantages for each final cell type. Current restrictions for human cell-based therapies have been related to technological limitations with regards to cellular proliferation capacity (simple culture conditions), maintenance of differentiated phenotype for primary human cell culture, transmission of communicable diseases and the consistency and stability of the selected population of cells depending on their isolation procedure. Cultured primary foetal cells from one organ donation meet the exigent and stringent technical aspects for development of therapeutic products. Master and working cell banks from one foetal organ donation can be developed in short periods of time and safety tests can be performed at all stages of cell banking.
Cell therapy has been proposed as a less invasive alternative or combined therapy for surgical procedures and tissue engineering of specific tissues. Several cell types have been investigated to be utilized in cell therapy: embryonic stem cells (ES), umbilical cord cells, foetal cells and adult stem cells (from bone marrow-haematopoitic stem cells or HSCs and marrow stem cells or MSCs) along with adipose tissue, platelets, placenta and amniotic fluid cells. As for any application in tissue engineering, the cell origin and type are essential aspects. Each type of cell requires different methods to manipulate their differentiation and self-renewal capabilities for specific therapies with various advantages and disadvantages.
Foetal cells have been used extensively in biology and medicine for many years without much public knowledge for their importance, especially in the development of necessary vaccines. Foetal cells are differentiated cells with high expansion, regeneration and low immunogenic properties. They can be isolated from foetal tissues, which follow embryonic stage after 9 weeks of development. Foetal skin cells offer an ideal solution for effective and safe cell therapy and tissue engineering for several reasons including; a) cell expansion capacity from one organ donation; b) minimal cell growth requirements; c) adaptation to biomaterials for delivery; and, d) resistance to oxidative stress. Foetal skin cells have extensive expansion possibilities as it requires only one organ donation (1-4 cm2 tissue) to create enough frozen cells to produce a bank capable of hundreds of thousands of treatments (i.e. for skin, over 35 billion fetal skin constructs 9×12 cm, can be produced from one dedicated cell bank). Also, cell culture requirements are minimal compared to stem or mesenchymal cell types. As the foetal skin cells are already differentiated and do not need to be directed or altered, the vast number of additional growth factors normally necessary are not needed for cell culture and expansion. For cell banking, careful selection of a donor and an extensive screening of both the donor and cultured cells to avoid transmissible viral, fungal or bacterial disease provide a safe and secure utilization of foetal cells for therapeutic usage. In addition, foetal cells, unlike neonatal, young or adult cells adapt particularly well to biomaterials allowing efficient and simple delivery to the patient. It has been shown that cells from donors (neonatal to adult) are not capable of efficient integration into various biomaterials and some biomaterials are, in fact, toxic to the cell. It is true that the scaffold is very important for tissue engineering, but the cell type is most probably the limiting factor. For processing of a final product for clinical delivery, both the homologous distribution and the rapidity of development of the final product are major significant advantages. When long culture periods are necessary as for autologous grafting or for the commercially available products to date, there is a non-negligible increased risk for contamination. It is also important to have a process that is consistent and easily repeated. By developing consistent cell banks with fetal cells, many of the risk factors can be eliminated for bringing safe and effective human cell-based therapies to the bedside.
Key elements including identity, purity, sterility, stability, safety and efficacy are recommended for cellular-based products. In all, the new regulations impose strict criteria for the production and the environment used for the production of cell-based products to be used in clinical trials and treatments. Current restrictions for human cell-based therapies have been related to technological limitations with regards to cellular proliferation capacity (simple culture conditions), maintenance of differentiated phenotype for primary human cell culture, transmission of communicable diseases and the consistency and stability of the selected population of cells depending on their isolation procedure. Cultured primary foetal cells from one organ donation meet the exigent and stringent technical aspects for development of therapeutic products. Master and working cell banks from one foetal organ donation can be developed in short periods of time and safety tests can be performed at all stages of cell banking. For therapeutic use, foetal cells can be used up to two thirds of their life-span in an out-scaling process and consistency for several biological properties includes protein concentration, gene expression and biological activity are ensured.
The relatively simple manipulation of foetal cells, related to their collection, culture expansion and storage has made foetal cells an attractive choice for cell therapy. Unlike ES cells, foetal cells do not form tumours and seem to lack immunogenecity when transplanted. In contrast with mesenchymal stem cells to date, foetal cells do not require feeder layers for growth or specific growth factors for differentiation. One organ donation is capable of producing a consistent, Master Cell Bank (MCB) that would be available for hundreds of thousands of patient treatments. The fully-defined consistent cell bank could easily be assessed for safety concerning any potential virus and pathogens in parallel to the original organ donation where serology and pathology are accomplished.
Primary cultures of foetal differentiated cells from specific tissues such as cartilage, tendon and skin which specific cell sources can be developed including chondrocytes (chondro-progenitors), skin fibroblast progenitors, and tendon progenitors determine the quality of the clinical cell bank developed. It is well accepted that the initial treatment of the tissue is of major importance to the physiological properties of the cells thereafter produced. The routine state-of-the-art in primary culture is to enzymatically digest the small pieces of tissue to liberate all live cells for cell culture. This is particularly used for “hard” tissues, but also for soft tissues, where multiple digestion steps are used routinely. By doing this, a completely different population of cells is liberated and cultured in the primary and secondary cell cultures (Carrascosa A, Audi L, Ballabriga A Pediatric Research 19:720-727, 1985; Roche S et al, Biomaterials 22:9-18, 2001; Bae H. et al., The Spine Journal Vol. 8, No. 5, pages 92S-93S, 2008; Reginato A. M. et al., Arthritis and Rheumatism, Vol. 37, No. 9, 1994).
However, it is also known that the enzymatic treatment causes inconsistencies, develops populations of cells with different morphologies, physiological properties, stability, and function (Diaz-Romero J, Gaillard J-P, Grogan P, Nesic, Trub T, Varlet P-M J Cellular Physiol 202:731-742, 2005).
The avascular, aneural and alymphatic nature of articular cartilage has made repair of this tissue a challenge for both surgeons and tissue engineers. A gold standard for osteochondral therapeutic strategies, especially for the choice of cell source remaining a central and controversial issue, is far from being determined. Adult mesenchymal stromal cells (MSCs) are, to date, the most used cell source, despite concerns of phenotypic homogeneity, reliability and stability.
Treatment of osteoarthritic defects needs to be improved as no satisfactory therapeutic solution exists to date. It is especially crucial to develop new solutions to avoid premature degeneration of the cartilage to avoid total joint replacement. Development of new cellular assisted surgical techniques is based on a defined cellular banked product that can meet the requirements for stringent therapeutic agent preparation.
Thus there is still a need to develop methods for producing new tissues such as tendon, cartilage, other musculoskeletal tissues, and skin, for use in the therapeutic strategies. More specifically there is a need to develop cell banks which provide more stable and uniform population of cells and to find an appropriate source of cells, that do not risk triggering an immune response, and that do not carry any infectious agents.